Porous sulfur particles can be produced for molten sulfur by introducing a molten sulfur stream into a cooling water stream at a velocity sufficient to produce a highly turbulent zone at the point of intersection as described in U.S. Pat. Nos. 3,637,371, 3,769,378 and 3,830,361, incorporated here by reference. The resulting particles are highly porous and present substantial internal and external surface area and pore volume. As a consequence of these characteristics, the particles themselves have numerous utilities including their use as soil sulfur or simply as a more convenient form in which to store, ship or otherwise handle sulfur intended for any use.
In addition to these qualities, I have discovered that the porous particles produced as described in the above referenced patents can be abraded or otherwise crushed to form very small, finely divided sulfur spheres suitable for use in compounding rubber or other elastomers or plastics, as soil sulfurs, in the production of sulfur suspensions, or in any other application in which finely divided sulfurs are required. The finely divided sulfur beads obtained by mild abrasion of the larger porous particles, while extremely small in themselves, are non-dusting and exhibit much less tendency to build up static charges than do finely divided sulfurs obtained by other methods, e.g., crushing block sulfur or the like. Finer subdivision results from more severe crushing.
One set of physical properties might not be the best for all of the uses in which these materials find application. For instance, it might be preferable to minimize particle comminution when the larger particles are used only for shipment or storage. Conversely, particles of lower crushing strength might be more preferred for conversion to small sulfur beads or for direct use as soil or compounding sulfurs when particle attrition is desirable. Hence, it would obviously be advantageous to be able to produce the larger porous particles having either high or low crushing strength depending upon the intended end use. I have now discovered that this objective can be achieved by controlling the temperature of the molten sulfur introduced into admixture with the water stream in the turbulent mixing zone.
It is therefore one object of this invention to provide an improved method for producing sulfur particles. It is another object to provide an improved method of producing porous sulfur particles which can be easily crushed or otherwise abraded to form finely divided sulfurs. Another object is the provision of an improved method for controlling the crushing strength of porous sulfur particles formed by the turbulent mixing of molten sulfur and water. Another object is the provision of a method for producing porous sulfur particles having either high or low relative crushing strength as desired.
Therefore, in accordance with one embodiment of this invention, the crushing strength of porous sulfur particles formed by the high velocity, turbulent mixing of molten sulfur and water streams is controlled by controlling the temperature of the molten sulfur injected into the water stream. This procedure affords several advantages. Porous particles of consistent crushing strength can be produced. Conversely, the sulfur temperature can be changed to obtain particles having either higher or lower crushing strength as desired. The range of temperature permissible is prescribed at the lower end by sulfur melting point, i.e., about 238.degree. F., and on the upper end by the point at which molten sulfur becomes excessively viscous and difficult to pump or force through orifices or nozzles, i.e., about 340.degree. F. Particles having high crushing strength can be obtained simply by operating at the higher end of this permissible range, e.g., at least about 280.degree. F.
Within the context of this disclosure and appended claims, the term crushing strength refers to resistance to crushing, or other types of mechanical attrition relative to the strength of particles produced under otherwise identical conditions although at a different temperature. Thus a particle produced from sulfur having a relatively high temperature, e.g., about 320.degree. F. will have a crushing strength greater than that of particles produced under otherwise identical conditions at a lower temperature such as 260.degree. F.
Crushing strength can be expressed in absolute units, e.g., psi. However, the absolute force applied to crush a given particle is; relative to the test by which it is determined. This is due to the influence of factors such as surface area, surface shape and friction coefficient, particle size, internal and surface structure, and the like. The influence of any one of these or other variables on can vary from one environment to the next. Thus, this property is best described in relative terms with respect to this invention which constitutes a method of controlling the crushing strength on a relative basis.
Not the least of the factors affecting crushing strength is particle size and, for that matter, the particle size distribution of a population of particles having some average hardness. As described in more detail hereinafter, particle size in turn is a function of other process variables such as water velocity, sulfur velocity, relative water/sulfur mass flow rates and the severity of turbulent mixing at the intersection of the sulfur and water streams which, at least to a large extent, controls the fragmentation and cooling rate of the sulfur stream.
Nevertheless, crushing strength can be controlled by controlling the molten sulfur temperature at a point within the operable range of about 238.degree. to about 340.degree. F. in proportion to the desired crushing strength. Particles obtained within this range of temperatures will usually have crushing strengths of about 350 to about 800 psi. Absent the influence of other variables such as particle size, crushing strength is a direct function of molten sulfur temperature. Thus crushing strength can be increased by increasing sulfur temperature or decreased by decreasing temperature. Thus these methods can be used to produce particles having crushing strength values, determined by the procedure described in the examples, of at least 500, preferably at least 550 psi at sulfur temperatures of at least 270.degree. F., preferably at least 300.degree. F. Conversely, particles having crushing strength of less than 500 psi, preferably less than 450 psi can be obtained by controlling sulfur temperature at a level below about 270.degree. F., preferably below 260.degree. F. These values are obtained by the analytical and mathematical procedures discussed hereinafter, and apply to particle sizes ranging between 8 to 14 mesh U.S. Standard Sieves.